Hippocampal network patterns of activity in the mouse

Abstract—Genetic engineering of the mouse brain allows investigators to address novel hypotheses in vivo. Because of the paucity of information on the network patterns of the mouse hippocampus, we investigated the electrical patterns in the behaving animal using multisite silicon probes and wire tetrodes. Theta (6–9 Hz) and gamma (40–100 Hz) oscil-lations were present during exploration and rapid eye move-ment sleep. Gamma power and theta power were comodu-lated and gamma power varied as a function of the theta cycle. Pyramidal cells and putative interneurons were phase-locked to theta oscillations. During immobility, consumma-tory behaviors and slow-wave sleep, sharp waves were present in cornu ammonis region CA1 of the hippocampus stratum radiatum associated with 140–200-Hz “ripples ” in the pyramidal cell layer and population burst of CA1 neurons. In the hilus, large-amplitude “dentate spikes ” occurred in asso-ciation with increased discharge of hilar neurons. The ampli-tude of field patterns was larger in the mouse than in the rat, likely reflecting the higher neuron density in a smaller brain. We suggest that the main hippocampal network patterns are mediated by similar pathways and mechanisms in mouse an